1. Field of the Invention
The present invention relates to a conductive elastomer composition, a conductive roller, and a conductive belt. More particularly, the conductive roller and the conductive belt composed of the conductive elastomer composition is used effectively as a charging roller, a developing roller, a toner supply roller, a transfer roller, a transfer belt, and the like for a copying machine, a printer, and the like to realize a low electric resistance and superior properties.
2. Description of the Related Art
It is necessary to allow the charging roller, the developing roller, the toner supply roller, the transfer roller, and the transfer belt for use in the copying machine and the printer to have an appropriate stable electric resistance value. To impart electric conductivity to the roller and the belt of this kind, the following two methods are known: an electroconductive elastomer containing a conductive filler such as powder of metal oxide or carbon black therein is used in one of them. An ionic-conductive elastomer such as urethane rubber, acrylonitrile-butadiene rubber (NBR), and epichlorohydrin rubber is used in the other of them.
The conductive roller or the conductive belt composed of the electroconductive elastomer containing the conductive filler has a problem that it has variations in the electric resistance value thereof, i.e., the conductive roller or the conductive belt does not have a constant electric resistance value. In the case where the carbon black is used as the conductive filler, there is no stable correlation between the addition amount of the carbon black and the volume resistivity of the electroconductive elastomer, and there is a region in which the electric resistance value of the conductive roller or the like changes rapidly owing to a slight change of the addition amount of the carbon black. Thus it is very difficult to control the electric resistance. In addition, the electric resistance value depends on an applied voltage.
Because it is difficult for the conductive filler to disperse uniformly in the elastomer, the electric resistance value has variations in the circumferential and widthwise directions of the conductive roller or the conductive belt. Even though a large variation of the electric resistance value is reduced, a variation of the electric resistance value as small as a μm order is still present. Recently, a high image quality is provided by using digital image processing technique and color image processing technique. Thus the ionic-conductive elastomer is used in preference over the electroconductive elastomer.
As conductive agents of the ionic-conductive elastomer, a conductive oligomer and a conductive plasticizer (Mn is less than 10000) containing a polyether structure such as polyethylene oxide are known. The ionic-conductive elastomer using these conductive agents bleed or bloom and is liable to stain a photosensitive member.
In addition to the above-described conductive agents, a method of using acrylonitrile-butadiene rubber (NBR) or a method of using urethane rubber is also known. However, these rubbers provide a volume resistivity of not less than 109.6 Ω·cm (electric resistance of roller is 108.2Ω). Thus these methods cannot be used for a transfer roller or a transfer belt for a color image processing apparatus which requires a comparatively low electric resistance. However, the elastomer containing only the NBR is not favorable in resistance to ozone.
In the case of the conductive roller or the conductive belt for a copying machine or a printer, a comparatively low trifluoromethanesulfonyl is required for the transfer belt and the transfer roller for a color copying machine or the like, the charging roller, the developing roller, the toner supply roller, and the like. Thus the use of only the above-described polymers are incapable of coping with this requirement. The level of the conductivity provided by these conductive agents is insufficient for preventing a silica tire and general rubber products from being charged.
Epichlorohydrin rubber or an ethylene oxide-propylene oxide-allyl glycidyl ether copolymer is used singly or in combination with other materials for the above-described use and some types of charging rollers, developing rollers, toner supply rollers, and the like. In addition, various proposals are made.
Various trials for increasing the ionization degree and realizing a lower electric resistance have been made by adding a quaternary ammonium salt containing perchloric acid ions or chloride ions to the ionic-conductive elastomer such as the acrylonitrile-butadiene rubber (NBR), the urethane rubber, epichlorohydrin rubber, a mixture formed by adding the epichlorohydrin rubber or the ethylene oxide-propylene oxide-allyl glycidyl ether copolymer thereto.
For example, in the rubber composition disclosed in Japanese Patent Application Laid-Open No. 9-132677, it is easy to impart conductivity to the rubber composition in which a quaternary ammonium salt of perchloric acid is added to the acrylonitrile-butadiene rubber or the epichlorohydrin rubber and control the electric resistance value.
However, the compression set of the rubber composition disclosed in Japanese Patent Application Laid-Open No. 9-132677 is not sufficiently reduced. That is, most of the chlorine of the quaternary ammonium salt has a secondary reaction, thereby deteriorating the compression set of the rubber composition outstandingly. Therefore the conductive roller or the conductive belt composed of the rubber composition has a problem in the durability and size stability thereof.
It is preferable to use a material having a low compression set for the conductive roller or the conductive belt and rubber products. Thus various proposals are made to solve this problem. However, a material having a preferable conductivity, a low hardness, and a low compression set has not been developed.